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| Titel |
N2O, NO, N2 and CO2 emissions from tropical savanna and grassland of northern Australia: an incubation experiment with intact soil cores |
| VerfasserIn |
C. Werner, K. Reiser, M. Dannenmann, L. B. Hutley, J. Jacobeit, K. Butterbach-Bahl |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 21 ; Nr. 11, no. 21 (2014-11-07), S.6047-6065 |
| Datensatznummer |
250117665
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| Publikation (Nr.) |
 copernicus.org/bg-11-6047-2014.pdf |
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| Zusammenfassung |
| Strong seasonal variability of hygric and thermal soil conditions are a defining environmental
feature in northern Australia. However, how such changes affect the soil–atmosphere exchange of
nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2) is still not well
explored. By incubating intact soil cores from four sites (three savanna, one pasture) under controlled
soil temperatures (ST) and soil moisture (SM) we investigated the release of the trace gas fluxes
of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to
denitrification was measured using the helium gas flow soil core technique. Under dry
pre-incubation conditions NO and N2O emissions were very low
(<7.0 ± 5.0 μg NO-N m−2 h−1; <0.0 ± 1.4 μg N2O-N m−2 h−1)
or in the case of N2O, even a net
soil uptake was observed. Substantial NO (max: 306.5 μg N m−2 h−1) and
relatively small N2O pulse emissions (max: 5.8 ±
5.0 μg N m−2 h−1) were recorded following soil wetting, but these pulses
were short lived, lasting only up to 3 days. The total atmospheric loss of nitrogen was generally dominated
by N2 emissions (82.4–99.3% of total N lost), although NO emissions contributed
almost 43.2% to the total atmospheric nitrogen loss at 50% SM and 30 °C ST
incubation settings (the contribution of N2 at these soil conditions was only 53.2%).
N2O emissions were systematically
higher for 3 of 12 sample locations, which indicates substantial spatial variability at site
level, but on average soils acted as weak N2O sources or even sinks.
By using a conservative upscale approach we estimate total annual emissions from savanna soils
to average 0.12 kg N ha−1 yr−1
(N2O), 0.68 kg N ha−1 yr−1 (NO) and 6.65 kg N ha−1 yr−1
(N2). The analysis of long-term SM and ST records makes it clear
that extreme soil saturation that can lead to high N2O and N2 emissions only
occurs
a few days per year and thus has little impact on the annual total.
The potential contribution of nitrogen released due to pulse events compared to the total annual emissions
was found to be of importance for NO emissions (contribution to total: 5–22%),
but not for N2O emissions. Our results indicate that the total gaseous release of nitrogen
from these soils is low and clearly dominated by loss in the form of inert nitrogen. Effects of seasonally
varying soil temperature and moisture were detected, but were found to be low due to the small amounts of available
nitrogen in the soils (total nitrogen <0.1%). |
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